X-Ray Scanner with Partial Energy Discriminating Detector Array

ABSTRACT

The present specification describes a scanning/inspection system configured as a dual-view system using dual-energy sensitive stacked detectors that are partially populated with multi-energy discriminating detectors for overall enhanced energy resolution and therefore improved discrimination of materials through better estimation of material physical properties such as density and effective atomic number.

CROSS-REFERENCE

The present application relies on U.S. Provisional Patent ApplicationNo. 61/749,838, entitled “X-Ray Scanner with Partial EnergyDiscriminating Detector Array” and filed on Jan. 7, 2013, for priority.The aforementioned application is herein incorporated by reference.

FIELD

The present specification relates to X-ray inspection systems. Moreparticularly, the present specification relates to a source, detectorand object configuration, whereby the energy transmitted through theobject being inspected is measured at improved energy resolutions.

BACKGROUND

Due to persistent security threats and the possibility of terroristactivities, there is a need for deploying high speed, high resolution,and accurate screening devices at places that are likely targets of suchactivities. In addition, there exists a requirement for screening ofbaggage and other items for explosives, contraband and other illicitmaterials. This requires a screening system which is capable ofdiscriminating between different materials based on one or more uniquefeatures of each material such as effective atomic number, chemicalstructure, physical density, among other variables.

Cabinet X-ray scanners are capable of performing automated threatdetection on articles of baggage and divested items by calculatingphysical properties of objects from the two-dimensional image generated.For example, material density can be estimated from at least twoco-planar projection views. Z-effective can be estimated from at leasttwo overlapping projection views acquired at different energy levels.Thus, increasing the number of views or number of energy levels permitsfor more precise estimations of physical properties such as materialdensity and Z-effective.

Conventional cabinet X-ray systems have a limited number of co-planarviews. It is highly desirable for commercial reasons to have as fewviews as necessary. Typically, a planar X-ray view consists of an X-raygenerator and a linear array of X-ray detectors, which constitutes amajority of the component costs in an X-ray scanner. Each additionalview increases the component cost of the scanner in an incrementalmanner. Thus, two views would imply twice the cost of a single view,three views would increase the cost three times, and so forth.Therefore, achieving desired imaging or automated detection performancewith the fewest number of views allows the lowest component cost.Increasing performance through other means, such as higher performancedetectors, becomes desirable because of the potential lower increase incomponent cost.

Further, increasing energy discrimination also has a detrimental impacton component cost. Commercially available X-ray detectors currentlypermit up to 128 channels of energy discrimination. Populating amultiple or even a single projection X-ray detector array with energydiscriminating detectors is commercially prohibitive. The cost of energydiscriminating detectors is significantly higher than conventionaldual-energy detector arrays. For example, a conventional single-viewX-ray scanner equipped with energy discriminating detectors would incura three-fold increase in component cost. Reducing the number of energydiscriminating detectors employed to increase performance becomes anattractive option, especially if the incremental increase in componentcost is less than doubling the cost of the machine, i.e. less than thecost of adding a second view.

For an application such as liquids screening, it is desirable to havethe full range of energy information permitting for a spectroscopicanalysis of the contents in the divested container. Therefore, someapplications present the opportunity to restrict the concept ofoperations such that only a portion of the projection view needs to bepopulated with multi-energy discriminating detectors in order to obtainimproved estimation of the physical properties necessary for effectivethreat detection. For example, with respect to the divestiture of liquidcontainers at an aviation security checkpoint for separate threatdetection analysis, only a portion of a bin or container need bescreened using multi-energy discriminating detectors.

Thus, what is needed is an X-ray scanner, having at least a single-view,with limited energy discriminating detector coverage that can meet orexceed the automated detection performance of a dual-view X-ray scannerand still have a lower component cost, thus achieving the trade-offbetween cost and performance.

Accordingly, there is a need for an X-ray system that has an overallimproved energy resolution to discriminate and therefore detect certainmaterials of interest.

SUMMARY

In one embodiment, the present specification describes a system forscreening objects, comprising: a) a receptacle for holding an object; b)a conveyor to move the receptacle through an inspection region; c) firstX-ray source for transmitting X-rays through the object for generating avertical X-ray projection view of the said object; d) a second X-raysource for transmitting X-rays through the object for generating ahorizontal X-ray projection view of the said object; e) a first set anda second set of transmission detectors for receiving the X-raystransmitted through the said object; and f) a third and a fourth set ofenergy discriminating detectors for receiving the X-rays transmittedthrough the said object, wherein said third and fourth set of energydiscriminating detectors are positioned such that they align with theobject within the receptacle.

In one embodiment, the present specification describes a method forscreening objects, comprising: a) providing a receptacle to hold andalign an object; b) moving the said receptacle through an inspectionregion using a conveyor; c) generating an X-ray projection view of thesaid object using an X-ray source; d) detecting X-rays transmittedthrough the said object using transmission detectors and at least oneenergy discriminating detector which is positioned such that it alignswith the object within the receptacle.

In one embodiment, the present specification describes a system forscreening objects, comprising: a) a receptacle for holding an object; b)a conveyor to move the receptacle through an inspection region; c) anX-ray source for transmitting X-rays through the object for generatingan X-ray projection view of the said object; d) a plurality oftransmission detectors for receiving the X-rays transmitted through thesaid object; and e) a plurality of energy discriminating detectors forreceiving the X-rays transmitted through the said object, wherein saidplurality of energy discriminating detectors are positioned such thatthey align with the object within the receptacle.

In another embodiment, the present specification describes a method forscreening objects, comprising: a) providing a receptacle to hold andalign an object; b) moving the said receptacle through an inspectionregion using a conveyor; c) generating an X-ray projection view of thesaid object using an X-ray source; d) detecting X-rays transmittedthrough the said object using a plurality of transmission detectors; ande) detecting X-rays transmitted through the said object using aplurality of energy discriminating detectors which are positioned suchthat they align with the object within the receptacle.

In one embodiment, the present specification describes a method forscreening objects, comprising: a) providing a receptacle to hold andalign an object; b) moving the said receptacle through an inspectionregion using a conveyor; c) generating a vertical X-ray projection viewof the said object using a first X-ray source; d) generating ahorizontal X-ray projection view of the said object using a second X-raysource; e) detecting X-rays transmitted through the said object using afirst set and second set of transmission detectors; and f) detectingX-rays transmitted through the said object using a third set and fourthset of energy discriminating detectors which are positioned such thatthey align with the object within the receptacle.

In another embodiment, the present specification describes a system forscreening objects, comprising: a) a receptacle for holding an object; b)a conveyor to move the said receptacle through an inspection region; c)a first X-ray source for transmitting X-rays through the object forgenerating a vertical X-ray projection view of the said object; d) asecond X-ray source for transmitting X-rays through the object forgenerating a horizontal X-ray projection view of the said object; e) afirst set and a second set of transmission detectors for receiving theX-rays transmitted through the said object; f) a third and a fourth setof energy discriminating detectors for receiving the X-rays transmittedthrough the said object, wherein said third and fourth set of energydiscriminating detectors are positioned such that they align with theobject within the receptacle; and g) a processor for receiving outputsignals from said first, second, third and fourth sets of detectors andoverlaying said output signals onto a visual image of the saidreceptacle and object.

In yet another embodiment, the present specification describes a methodfor screening objects, comprising: a) providing a receptacle to hold andalign an object; b) moving the said receptacle through an inspectionregion using a conveyor; c) generating a vertical X-ray projection viewof the said object using a first X-ray source; d) generating ahorizontal X-ray projection view of the said object using a second X-raysource; e) detecting X-rays transmitted through the said object using afirst and second set of transmission detectors; f) detecting X-raystransmitted through the said object using a third and fourth set ofenergy discriminating wherein said third and fourth set of energydiscriminating detectors are positioned such that they align with theobject within the receptacle; and g) processing the output signals fromsaid first, second, third and fourth sets of detectors to form a visualimage of the said receptacle and object.

In one embodiment, the receptacle is a tray further comprising a foaminsert that has at least one channel to align the said object forscreening. In one embodiment, the object is a LAG item.

In one embodiment, the first and second transmission detectors aredual-energy sensitive stacked detectors while the third and fourthenergy discriminating detectors are fabricated from high-Z semiconductormaterials including cadmium-telluride (CdTe), cadmium-zinc-telluride(CZT), mercury iodide (HgI₂), selenium (Se), lead iodide (PbI₂), galliumarsenide (GaAs).

The aforementioned and other embodiments of the present specificationshall be described in greater depth in the drawings and detaileddescription provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present specificationwill be further appreciated, as they become better understood byreference to the detailed description when considered in connection withthe accompanying drawings:

FIG. 1A is a side perspective view of the inspection system of thepresent specification showing a source irradiating an object to obtain avertical projection view of the object;

FIG. 1B is a side perspective view of the inspection system of thepresent specification showing a source irradiating the object to obtaina horizontal projection view of the object;

FIG. 2A shows a receptacle of the present specification in the form of atray holding objects to be scanned; and

FIG. 2B is an X-ray image of the tray of FIG. 2A obtained using adual-view embodiment of the inspection system of the presentspecification.

DETAILED DESCRIPTION

The present specification is directed towards scanning objects forthreat/contraband detection. In one embodiment, the scanning/inspectionsystem of the present specification is configured for screening objectsat aviation security checkpoints. However, in alternate embodiments, thescanning/inspection system of the present specification is deployable atany such sites/places that are likely to be targets of terroristactivities—such as, border security checkpoints, entrances to buildingsor other vulnerable premises, concert venues, sports venues, and thelike.

In one embodiment, the scanning/inspection system of the presentspecification is configured as a single-view system using dual-energysensitive stacked detectors that are partially populated withmulti-energy discriminating detectors for overall enhanced energyresolution and therefore improved discrimination of materials throughbetter estimation of material physical properties such as density andeffective atomic number.

In one embodiment, the scanning/inspection system of the presentspecification is configured as a dual-view system using dual-energysensitive stacked detectors that are partially populated withmulti-energy discriminating detectors for overall enhanced energyresolution and therefore improved discrimination of materials throughbetter estimation of material physical properties such as density andeffective atomic number.

In one embodiment, the transmission detectors are dual-energy sensitivestacked detectors while the energy discriminating detectors arefabricated from high-Z semiconductor materials includingcadmium-telluride (CdTe), cadmium-zinc-telluride (CZT), mercury iodide(HgI₂), selenium (Se), lead iodide (PbI₂), gallium arsenide (GaAs).

In accordance with an aspect of the present specification, a“receptacle” can be defined as an open, closed or closable vessel orcontainer for housing objects that need to be scanned. The receptacleensures that the objects therein are aligned, restricted, constrained orpositioned to occupy a predetermined or predefined volumetric space withreference to the source, detector and conveyor configuration of aninspection system. In one embodiment the receptacle is an open tray. Inanother embodiment, the receptacle is a box with a closable lid.

In accordance with one embodiment, the size of the receptacle is on theorder of 550 mm wide ×685 mm long×140 mm high.

In alternate embodiments, the receptacle is a piece of luggage orbaggage containing objects that are not necessarily placed, positioned,oriented, or restricted in a predetermined fashion relative to theinspection system. Instead, the objects are placed in a random fashionas would be expected in typical luggage/baggage.

In accordance with an aspect of the present specification, an “object tobe screened” can be defined as an open, closed or closable vessel,container or housing containing liquid or gel-based items that resembleliquid or gel-based explosives/threats such as liquid, aerosol and gelitems (hereinafter referred to as “LAG” items). Categories of LAG itemstypically found in passenger carry-on baggage include, but are notlimited to, alcohol/perfume/deodorants, drinks, foods, householdproducts, medicines, toiletries, and the like. Prior to screening, LAGitems are typically divested from baggage, luggage or personal effectsand placed in a receptacle for scanning. In accordance with oneembodiment, the object is of a size range that allows it to be placed inthe receptacle. In one embodiment, volume ranges for a typical vessel tobe screened are from 100 mL to 2000 mL.

In alternate embodiments, the object comprises any solid, powder orplastic-based threat or contraband items known to persons of ordinaryskill in the art and is not limited to LAG items.

The present invention is directed towards multiple embodiments. Thefollowing disclosure is provided in order to enable a person havingordinary skill in the art to practice the invention. Language used inthis specification should not be interpreted as a general disavowal ofany one specific embodiment or used to limit the claims beyond themeaning of the terms used therein. The general principles defined hereinmay be applied to other embodiments and applications without departingfrom the spirit and scope of the invention. Also, the terminology andphraseology used is for the purpose of describing exemplary embodimentsand should not be considered limiting. Thus, the present invention is tobe accorded the widest scope encompassing numerous alternatives,modifications and equivalents consistent with the principles andfeatures disclosed. For purpose of clarity, details relating totechnical material that is known in the technical fields related to theinvention have not been described in detail so as not to unnecessarilyobscure the present invention.

FIG. 1A shows a side perspective view of an embodiment of an energydiscriminating partial array inspection system 100 of the presentspecification in which a single-view vertical projection is provided.System 100 comprises a support frame 105 holding a first X-ray source110 with focusing means, such as a collimating slit, and a firstenhanced array 119 of stacked detectors 120 populated with at least onemulti-energy discriminating detector 122 in accordance with an aspect ofthe present specification. In one embodiment, the detectors are placedin an L-shaped configuration; however, other configurations may beacceptable provided that the detectors are appropriately positionedrelative to the inspection region and X-ray source.

It should be appreciated that the detector array of the presentspecification is known as a folded “L” detector configuration, and ismade from multiple detector modules 120, 122. Each detector module ispositioned at a different angle so as to be perpendicular to the X-rayfan beam. A typical small tunnel X-ray scanner will use approximately 10detector modules. Not every detector module needs to be replaced with anenergy discriminating detector module for the desired performanceimprovement. The projection of the container onto the image arraydetermines which detector modules need to be of the energydiscriminating variety. Referring to FIG. 1A, two energy discriminatingmodules 122 are shown to provide the advantages of the presentspecification.

FIG. 1B is a side perspective view of an embodiment of an energydiscriminating partial array inspection system 100 of the presentspecification in which a single-view horizontal projection is provided.System 100 comprises a support frame 105 holding a second X-ray source115 with focusing means, such as a collimating slit, and an enhancedarray 124 of stacked detectors 125 partially populated with at leastone, and preferably two, multi-energy discriminating detectors 127 inaccordance with an aspect of the present specification. In oneembodiment, the detectors are placed in an L-shaped configuration;however, other configurations may be acceptable provided that thedetectors are appropriately positioned relative to the inspection regionand X-ray source. The energy discriminating detectors must be positionedto provide the image of the container under inspection. The informationcontained within the image of the container is used for the analysis anddetermination of the contents.

Referring to FIGS. 1A and 1B simultaneously, an inspection area/regionin the form of a tunnel is defined between the sources and detectors toallow a receptacle 135 to be transported through using a conveyor 130.The receptacle 135 holds an object that is to be screened. It should benoted by those of ordinary skill in the art that while the presentembodiment of the system 100 is a dual projection view system comprisingtwo sources, in alternate embodiments the system 100 is a singleprojection view system comprising a single source whereas in stillfurther embodiments the system 100 is a multi-projection view systemcomprising more than two sources. In one embodiment, the dual projectionview system of the present invention employs 10 detector modules withindetector array 119 for the vertical view and 9 detector modules withindetector array 124 for the horizontal view.

Referring to FIGS. 1A and 1B simultaneously, in one embodiment, aminimum of two energy discriminating modules 122, 127, respectively, areemployed in each detector array for significant enhancement of thephysical property measurement of the system of the present specificationin order to obtain a complete image of the container. Further, theembodiments shown in FIGS. 1A and 1B can be combined to provide adual-view embodiment, as shown in FIG. 2B.

During screening, the sources project fan beams of X-rays onto thereceptacle 135 such that the radiation-fans intersect the conveyor 130substantially perpendicular relative to the conveyor surface. As shownin FIG. 1A, in one embodiment, source 110 is positioned to form avertical projection view 140. In accordance with another aspect of thepresent specification, the receptacle 135 ensures that the position ofthe object to be screened is aligned or restricted relative to thesource, detector and conveyor configuration so that portion 142 of thefan beam projection views 140 are sensed by the multi-energydiscriminating detectors 122 to obtain improved estimation of thephysical properties of the object for effective threat detection. Thisis described in greater detail below with respect to FIG. 2B.

As shown in FIG. 1B, in one embodiment, source 115 is positioned to forma horizontal projection view 145. In accordance with another aspect ofthe present specification, the receptacle 135 ensures that the positionof the object to be screened is aligned or restricted relative to thesource, detector and conveyor configuration so that portion 147 of thefan beam projection views 145 are sensed by the multi-energydiscriminating detectors 127 to obtain improved estimation of thephysical properties of the object for effective threat detection.

FIG. 2A shows an embodiment of an exemplary receptacle of the presentspecification in the form of a tray 205. The tray 205 comprises, in oneembodiment, a foam insert 210 further comprising at least one channelfor aligning at least one object 215 in an optimum position forscreening. The insert is, in one embodiment, a mechanical component toensure the container is in the optimum position for screening, whichincludes not having contact with other high density objects and mostlylifting the container off the belt for a cleaner view in the image. Theinsert does not need to be made of foam; it can be made of any lowerdensity material than the container or contents for which screening isdesired. In one embodiment, it is possible to make the plastic tray suchthat it can present the container for analysis, thus obviating the needfor an insert.

FIG. 2B shows a dual-view X-ray image of the tray 205 while beingtransported on a conveyor belt. In accordance with an embodiment of thepresent specification, dimension B is the width of the conveyor belt 220(the tunnel walls being very close to the edge of the belt). The tray205 is wide enough such that is does not permit side-to-side movement.The width of the tray 205 coupled with the size and position of thechannel in the foam insert 210 limits the region that can be occupied bythe object 215 to a dimension A. Dimension A defines the minimum regionsof the imaging arrays (for the respective projection views) that arerequired to be populated with energy discriminating detectors to enablea more precise physical property measurement (shown as portions 142, 147in FIGS. 1A and 1B, respectively). In one embodiment, dimension A has amaximum of 125 mm at the belt, and when projected on the detector arraythis maximum dimension will occupy 20% of the imaging array whiledimension B is 575 mm.

In one embodiment, the at least one object 215 is a LAG item that isdivested from baggage/luggage and put in the tray 205 for scanningHowever, in alternate embodiments, object 215 can be any item that isrequired to be scanned for threat resolution. In one embodiment, theobject 215 is a piece of luggage/baggage and is scanned as-is, whilebeing conveyed, without the need for putting the luggage/baggage orobjects divested from the luggage/baggage in the tray 205.

Referring back to FIGS. 1A and 1B, the stacked detectors 120, 125generate dual energy scan data in accordance with one embodiment. Asknown to persons of ordinary skill in the art, stacked detectorscomprise a first detector positioned to detect more of the lower energy,or the softer X-ray photons, and a second detector positioned to detectthe balance of the energy, namely the higher energy, or the harderphotons. The second detector is typically positioned behind the firstdetector. The low energy and high energy measurements are combined in asuitable way using a series of calibration measurements derived fromdual energy measurements taken of identified organic and metallicmaterials of known thicknesses and result in the display of images,including organic only or metal only images. The first and seconddetectors consist of linear arrays of silicon photodiodes covered withscintillation material, which produce light when exposed to X-rays. Thelight is detected by the photodiodes that produce corresponding photocurrent signals. The detected data are converted to digital format,corrected for detector gain and offset, and then stored for processing.In another embodiment, detectors 120, 125 are conventional single energyarrays as known to persons of ordinary skill in the art.

In one embodiment, the multiple-energy discriminating detectors 122, 127are solid state detectors made from semiconductor materials such ascadmium-telluride (CdTe), cadmium-zinc-telluride (CZT), mercury iodide(HgI₂), selenium (Se), lead iodide (PbI₂), gallium arsenide (GaAs) orany other high-Z material that enables the detectors to be operable atroom temperature. These detectors have high energy resolution, ascompared to the dual energy stacked detectors and are direct conversiondevices (that is, convert radioactive particles, such as photons,directly into electronic signals).

In one embodiment, a low-noise, low-power, multi-channel readoutapplication-specific integrated circuit (ASIC) is used for theacquisition of scan data. Each channel of the ASIC has an energydiscriminating circuit and a time discriminating circuit. The ASIC alsohas built-in analog to digital converters (ADCs), or digitizers, todigitize the signal from energy and timing sub-channels. Variation inthe digital output of the ASIC is tracked from a reference signal outputto generate correction coefficients. The correction coefficients may bethen applied to subsequent digital outputs to eliminate or reducetemperature-induced error.

System 100 also comprises at least one processor (such as a computer)having access to a memory for storing programmatic instructions in theform of software and/or firmware. The at least one processor may belocal to, or remote from, the X-ray source and detectors. Similarly, thememory and programmatic instructions may be local to, or remote from,the X-ray source and detectors.

In a single-view configuration, when the programmatic instructions areexecuted, the at least one processor: a) reconstructs a combined imagefrom scan data generated by the detectors 120, 122 wherein each pixelwithin the image represents an associated mass attenuation coefficientof the object under inspection at a specific point in space and for aspecific energy level; b) fits each of the pixels to a function todetermine the mass attenuation coefficient of the object underinspection at the point in space; and c) uses the function toautomatically determine the identity or threat status of the objectunder inspection.

In a dual-view configuration, when the programmatic instructions areexecuted, the at least one processor: a) reconstructs a combined imagefrom scan data generated by the detectors 120, 122, 125 and 127, whereineach pixel within the image represents an associated mass attenuationcoefficient of the object under inspection at a specific point in spaceand for a specific energy level; b) fits each of the pixels to afunction to determine the mass attenuation coefficient of the objectunder inspection at the point in space; and c) uses the function toautomatically determine the identity or threat status of the objectunder inspection.

In one embodiment, the function yields a relationship between massattenuation coefficients and logarithmic values of energy. The functionrelates the energy response of the detector arrays at each energy withina range of energies multiplied by a function of the object's linearattenuation coefficient and density. Determining the identity or threatstatus of the object under inspection is performed by comparing theobject's linear attenuation coefficient function to data comprisinglinear attenuation coefficient functions of predefined materials. Thecomparison yields a fit comparing the relationship between massattenuation coefficients and logarithmic values of energy obtained fromthe object under inspection to pre-computed material data for knownmaterials. This allows for improved discrimination of materials throughbetter estimation of material physical properties such as density andeffective atomic number. Based on the comparison, pixels which aredetermined to qualify as potential threat materials are automaticallyhighlighted within the image.

Since the multiple-energy discriminating detectors possess higher energyresolution compared to the remaining stacked detectors, persons ofordinary skill in the art would appreciate that the use of multipleenergy discriminating detectors enhances the physical propertymeasurement of the system and therefore improves the automated threatdetection capabilities.

Referring again to FIGS. 1A and 1B, during operation, when thereceptacle containing the object under inspection is moving through thetunnel on conveyor 130 and passing through the X-ray projection fanbeams of sources 110, 115, the detector modules 120, 122, 125 and 127are sampled repetitively. The projection or scan data pertaining to thedual energy stacked detectors 120, 125 as well as the multi-energydiscriminating detectors 122, 127 are displayed as an integrated imageoutput such that there is no perceivable difference in the region of theimage owing to the multi-energy discriminating detectors as opposed tothe stacked detectors.

The above examples are merely illustrative of the many applications ofthe system of present invention. Although only a few embodiments of thepresent invention have been described herein, it should be understoodthat the present invention might be embodied in many other specificforms without departing from the spirit or scope of the invention.Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive, and the invention may be modifiedwithin the scope of the appended claims.

We claim:
 1. A system for screening objects, comprising: a) a receptaclefor holding an object; b) a conveyor to move the receptacle through aninspection region; c) a first X-ray source for transmitting X-raysthrough the object for generating a vertical X-ray projection view ofthe said object; d) a second X-ray source for transmitting X-raysthrough the object for generating a horizontal X-ray projection view ofthe said object; e) a first set and a second set of transmissiondetectors for receiving the X-rays transmitted through the said object;and f) a third and a fourth set of energy discriminating detectors forreceiving the X-rays transmitted through the said object, wherein saidthird and fourth set of energy discriminating detectors are positionedsuch that they align with the object within the receptacle.
 2. Thesystem of claim 1 wherein the receptacle is a tray further comprising afoam insert that has at least one channel to align the said object forscreening.
 3. The system of claim 1 wherein the first and secondtransmission detectors are dual-energy sensitive stacked detectors. 4.The system of claim 1 wherein the third and fourth energy discriminatingdetectors are fabricated from high-Z semiconductor materials includingcadmium-telluride (CdTe), cadmium-zinc-telluride (CZT), mercury iodide(HgI₂), selenium (Se), lead iodide (PbI₂), gallium arsenide (GaAs). 5.The system of claim 1 wherein the said object is a liquid, aerosol, gel(LAG) item.
 6. The system of claim 1 further comprising a processor forreceiving output signals from said first, second, third and fourth setsof detectors and overlaying said output signals onto a visual image ofthe said receptacle and object.
 7. A method for screening objects,comprising: a) providing a receptacle to hold and align an object; b)moving the said receptacle through an inspection region using aconveyor; c) generating a vertical X-ray projection view of the saidobject using a first X-ray source; d) generating a horizontal X-rayprojection view of the said object using a second X-ray source; e)detecting X-rays transmitted through the said object using a first setand second set of transmission detectors; and f) detecting X-raystransmitted through the said object using a third set and fourth set ofenergy discriminating detectors which are positioned such that theyalign with the object within the receptacle.
 8. The method of claim 7wherein the said receptacle is a tray further comprising a foam insertthat has at least one channel to align the said object for screening. 9.The method of claim 7 wherein the said first and second set oftransmission detectors are dual-energy sensitive stacked detectors. 10.The method of claim 7 wherein the said third and fourth set of energydiscriminating detectors are fabricated from high-Z semiconductormaterials including cadmium-telluride (CdTe), cadmium-zinc-telluride(CZT), mercury iodide (HgI₂), selenium (Se), lead iodide (PbI₂), galliumarsenide (GaAs).
 11. The method of claim 7 wherein the said object is aliquid, aerosol, gel (LAG) item.
 12. The method of claim 7 furthercomprising the step of processing the output signals from said first,second, third and fourth sets of detectors to form a visual image of thesad receptacle and object.
 13. A system for screening objects,comprising: a) a receptacle for holding an object; b) a conveyor to movethe receptacle through an inspection region; c) an X-ray source fortransmitting X-rays through the object for generating an X-rayprojection view of the said object; d) a plurality of transmissiondetectors for receiving the X-rays transmitted through the said object;and e) a plurality of energy discriminating detectors for receiving theX-rays transmitted through the said object, wherein said plurality ofenergy discriminating detectors are positioned such that they align withthe object within the receptacle.
 14. The system of claim 13 wherein thereceptacle is a tray further comprising a foam insert that has at leastone channel to align the said object for screening.
 15. The system ofclaim 13 wherein the plurality of transmission detectors are dual-energysensitive stacked detectors.
 16. The system of claim 13 wherein theplurality of energy discriminating detectors are fabricated from high-Zsemiconductor materials including cadmium-telluride (CdTe),cadmium-zinc-telluride (CZT), mercury iodide (HgI₂), selenium (Se), leadiodide (PbI₂), gallium arsenide (GaAs).
 17. The system of claim 13wherein the said object is a liquid, aerosol, gel (LAG) item.
 18. Thesystem of claim 13 further comprising a processor for receiving outputsignals from said plurality of detectors and overlaying said outputsignals onto a visual image of the said receptacle and object.